Display storage tube with solenoidal focus and simultaneous deflection of writing and flood beams



United States Patent O 3,281,621 DISPLAY STORAGE TUBE WITH SOLENOIDALFOCUS AND SIMULTANEOUS DEFLECTION F WRITING AND FLOOD BEAMS Robert H.Clayton, Fort Wayne, Ind., assignor to International Telephone andTelegraph Corporation, Nutley, NJ., a corporation of Maryland Filed Feb.11, 1964, Ser. No. 343,975 12 Claims. (Cl. 315-12) This inventionrelates generally to signal-to-image display storage tubes and moreparticularly to a display storage tube in which both the image andscanning sections are focused by a continuous axial magnetic field.

Conventional signal-to-image display storage tubes are of the cathoderay type and comprise a phosphor display screen, a storage screen, awriting gun, and a flood gun. The storage screen conventionallycomprises a fine mesh metal screen coated on the side facing the writingand flood guns with dielectric material having secondary emissionproperties. The writing gun directs a pencil electron beam toward thestorage screen, the pencil beam being modulated in accordance with aninput electrical signal and scanned over the dielectric surface of thestorage screen. Scanning of the modulated pencil beam over the storagescreen writes a charge pattern on the storage screen corresponding tothe input signal. The flood gun directs a low velocity flood beam ofelectrons toward the storage screen, the flood beam electrons passingthrough the apertures in the storage screen to the display screen beingmodulated by the incremental charges on the storage screen therebyproviding Va visible image on the displayV screen corresponding to thecharge pattern on the storage screen.

In conventional signal-to-image display storage tubes, the floodelectrons are neither focused nor collimated as they approach thestorage screen. Each aperture in the storage screen in essence forms anindividual electron lens which focuses the flood electrons in a planevery close to the plane of the storage screen with the result that theflood electrons subsequently diverge to a large circle of confusion atthe phosphor display screen, thus adversely affecting the resolution ofthe displayed image. It is therefore desirable to provide asignal-to-image display storage tube in which the flood electrons arereconverged or refocused in the image section of the tube, i.e., betweenthe storage screen and the display screen, thereby to improve theresolution of the displayed image.

It is accordingly an object of the invention to provide an improvedsignal-to-image display storage tube.

Another object of the invention is to provide an improvedsignal-to-image display storage tube providing improved resolution ofthe displayed image.

A further object of the invention is to provide an improvedsignal-to-image display storage tube employing axial magnetic focusingof the flood electrons in the image section.

Solenoidal magnetic fields have been employed in storage image convertertubes, such as that described and illustrated in Patent No. 2,983,836 toPaul Rudnick and Richard K. Orthuber and assigned to the assignee of thepresent application, to focus an electron image formed at the plane of astorage screen into the plane of a phosphor display screen. In suchstorage image tubes, however, the charge pattern which is written ontothe storage screen is derived from an extended area photocathode whichis arranged essentially parallel to the plane of the storage screen; theinput to the storage image tube is optical. In the signal-to-imagedisplay storage tube, however, the input is a time-based signal employedto modulate the pencil or writing electron beam which must be scannedover the storage screen in order to generate the charge 3,281,621Patented Oct. 25, 1966 pattern. Subjection of the image section of thetube alone to an axial or Solenoidal magnetic focusing field wouldprovide the desired focusing of the stored electron image, however, theend effects of such focusing field would prevent effective scanning ofthe writing beam over the storage screen or flooding of the storagescreen with the flood beam. In conventional signalsto-image displaystorage tubes, only the writing beam is scanned over the storage screen,and if a Solenoidal magnetic focusing field is extended throughout theentire length of the tube, conventional methods of writing beamdeflection are ineffective to provide the requisite scanning -of thewriting beam over the storage screen.

I have found that the flood beam in both the image and the scanningsections of a signal-to-image display storage tube may be focused by acontinuous Solenoidal magnetic field extending throughout the length ofthe tube by providing concentric writing and flood electron beams and byproviding magnetic deflection fields for simultaneously deflecting bothbeams. This axial magnetic focusing of the flood beam in both thescaanning and image sections of the tube provides not only theanticipated improvement in resolution in the image section, but anunexpected improvement in resolution of the stored image on the storagescreen, the result being the provision of a displayed image having aresolution significantly improved over that provided by conventionalsignal-to-image display storage tubes.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

The single figure of the drawing schematically illustrates the improvedsignal-to-image display storage tube of the invention.

Referring now to the drawing, the improved signal-toimage displaystorage tube of the invention, generally indicated at 10 comprises aconventional axially-elongated evacuated envelope 11 having aconventional phosphor display screen 14 deposited on the inner surfaceof faceplate 15 which closes one end of the envelope. A conventionalcharge storage screen 16 is positioned in the envelope 11 between thedisplay screen 14 and the other end 17 of the tube, the storage screenbeing in a plane parallel with that of the display screen 14 and normalto the longitudinal axis of the tube. Storage screen 16 may inaccordance with conventional practice comprise a fine mesh metal backingscreen 18 having its side which faces end 17 of the envelope 11 coatedwith suitable dielectric material having secondary emission properties,as at 19. A conventional collector screen 20 is positioned in theenvelope 11 between storage screen 16 and end 17 for collectingsecondary electrons emitted from the dielectric coating 19 of thestorage screen, as is well known to those skilled in the art.

A pencil or writing beam electron gun 22 is provided in the envelope 11adjacent end 17 thereof and comprises a cathode sleeve 23 concentricwith the longitudinal axis of the tube and having a heater 24 therein, aplanar control grid 25 concentric with the tube axis, and normalthereto, and a planar anode 26 likewise concentric with the tube axisand normal thereto, control grid 25 and anode 26 respectively havingcentral apertures 27, 28 formed therein concentric with the `tube axis.Heater 24 is connected to terminals 29 for connection to a suitablesource of energizing potential, cathode 23 and anode 26 are respectivelyconnected to terminals 30, 32 for connection to suitable potentials, andcontrol grid 25 is connected to input terminal 33 adapted to beconnected to receive a time-based electrical input signal for modulatingthe pencil or writing electron beam which is provided by the writing gun22 and directed toward the storage screen 16.

A flood electron gun 34 is provided comprising an extended area planarcathode 35 concentric with and normal to the longitudinal axis of thetube, and a suitable heater 36. Cathode 35 has a central aperture 37concentric with the longitudinal axis of the tube and with the writinggun- 22 through which the writing beam passes. A sleeve portion 38 isformed on cathode 35 concentric With the axis of the tube and exten-dingtoward anode 26 of the Writing gun 22. Heater 36 of the flood =gun 34 isconnected to terminals 39 for connection to a suitable source ofenergizing potential and cathode 35 is connected to terminal 40 which isadapted to be connected to a suitable source of potential.

In order to provide planar accelerating equipotentials for the floodcathode 35, suitable conductive coatings 42, 43, and 44 are formed onthe interior surface of the envelope 11 between the flood cathode 35 andthe collector screen 20, coatings 42, 43, 44 being respectivelyconnected to terminals 45, 46 and 47 adapted to be oonnected to suitablepotentials; while separate conductive CII electrodes or coatings 42, 43,44 are shown, the planar accelerating equipotentials may be provided bya continuous conductive coating or electrode.

It will now be seen that a pencil electron beam, shown by the dashedline 48 is provided by the writing gun 22 and that a concentric floodbeam, having lower electron velocity than lthe writing beam 48 isprovided by the flood ygun 34, as shown by the dashed line 49.

In order to provide for deflection of both the writing electron beam 48and the flood electron beam 49 and thus to scan both beams over thestorage screen 16, vertical and horizontal magnetic deection coils oryokes 50, 52 are respectively provided on the exterior of envelope 11between the flood gun 34 and the collector screen 20. Deection yokes 50,52 are connected to terminals 53, 54 for connection to suitable sourcesof sweep voltages to provide the desired type and rate ofscanning, forexa-mple raster scanning. It will be seen that the magnetic fieldsprovided by the deection yokes 50, 52 are respectively transverse withrespect to the longitudinal axis of the tube and thus, assuming that thedirection of the field provided by the vertical deflection yoke 50 is asshown by the arr-ow 55, it will be seen that both the writing beam 48and the flood -beam 49 will be deected as at 56, 57.

In order to focus the flood beam 49 in the image section 59 of the tube,and to focus the writing beam 48 in the writing section 58 of the tube,a solenoid coil 60 is provide-d surrounding envelope 11 and thedeflection yokes 50, 52, and extending axially between ends 14, 17 ofthe envelope. Solenoid coil 60 has leads connected to terminals 62adapted to be connected to a suitable source of direct current voltageand provides a solenoidal magnetic -ield extending axially through thetube parallel with its longitudinal axis, as shown by the dashed line63; the polarization of the solenoid coil 60 and of the axial magneticfield provided thereby is not important.

In order to provide optimum resolution of the displayed image on thedisplay screen 14, it is necessary that the flood electrons arrive atthe display screen 14 after an integral number of full loops of focus,preferably one (l) loop of focus between the storage screen 16 and thedisplay screen 14. This may be accomplished by selection of the axiallength of the image section 59 lbetween the storage screen 16 and thedisplay screen 14 and/or adjustment of the strength of the magneticfield provided by the solenoid coil 60. However, in onder to reduce theaxial length of the image section 59 and/or reduce the focusing fieldstrength, a field mesh 64 is provided in the image section 59 adjacentthe -display screen 14 and parallel therewith. Field mesh 64 isconnected to terminal 65 which is adapted to be connected to a suitablesource of potential, the field mesh 64 thus serving to decrease theaverage velocity of the liood electrons from the storage screen 16 tothe display screen 14 and in turn increasing their transit time. Inorder further to control the transit time of the iiood electrons in theimage section 59, a plurality, shown here as being six (6) in number, ofaxially spaced ring electrodes 66, 67, 68, 69, 70, and 72 are providedin the image section 59 between the storage screen 16 and the field mesh64, the ring electrodes 66-72 being respectively connected to terminals73, 74, 75, 76, 77 and 78 respectively adapted'to be connected t-opotentials increasing in equal steps from the storage screen 16 towardthe field mesh 64.

In order to provide optimum resolution of the charge image written ontothe storage screen 16 by the writing beam 48, it is further desirablethat the writing beam electrons arrive at the dielectric surface 19 ofthe storage screen 16 after an integral number of full loops of focus,preferably a multiple number of loops, such as three (3) to five (5);this is preferably accomplished by selection of the axial length of thewriting section 58 of the tube.

Display screen 14 is connected to terminal 79 adapted to be connected toa suitable source ofhigh voltage, collector screen 20 is connected toterminal 80` adapted to be connected to a suitable source of collectorpotential, and the backing screen 18 of the storage screen 16 isconnecte-d to terminal 82 adapted t-o be selectively connected tosuitable sources of writing and erasing potentials, as is well known tothose skilled in the art.

In a specific em-bodiment of the tube of the invention in which asolenoid focus coil 68 is energized to provide a field strength of sixty(60) gauss, satisfactory operation may be provided by the application ofthe following potentials: i

Display screen 14 10,000 volts Field mesh 64 400 volts Ring electrodes66-72 0 to 400 volts in Backing screen 18 10 volts P) (erase).

Collector screen 20 150 volts (-1-).

Wall coatings 42, 43, 44 100 vol-ts (-1-).

'Flood cathode 35 Ground.

Writing gun anode 28 Ground.

Writing -gun cathode 23 400 volts Writing gun control grid 25 400 voltsto 500 volts It will now be seen that the use of magnetic deection forboth the writing and liood electron bea-ms permits the extension of theaxial focusing field throughout the entire length of the tube since bothelectron beams will follow the curvature of the composite fieldcomprising the superimposed axial focus and transverse deflectionfields. It will be observed by reference to the above tabulation oftypical potentials that the writing beam is of relatively low velocitywhich permits its deiiection in the presence of the axial focusingfield; the usual relatively high velocity or stiff writing beam wouldrequire substantially Igreater deflection fields for its deflection inthe presence of the focusing field.

While the flood beam 49 is scanned over the storage screen 16 and thedisplay screen 14 simultaneously with the scanning of the writing beam,in contrast with conventional signal-to-image display storage tubes inwhich the flood beam continuously lioods the entire area of the storagescreen, it has been found that if the frame rates for writing areflicker free, i.e., any rate in excess of approximately twenty (20)frames per second, human visual persistence will mask the differencebetween the display resulting fr-om the scanned fiood beam and the.conventional static flood beam display so that simultaneous writing anddisplay. may be employed. Erasure of the store-d image on the storagescreen 16 may be accomplished during the active scanning time by theapplication of erase pulses having a repetition rate Wh1ch is somemultiple of the scanning frequency or a continuous erase pulse may beapplied during retrace.

A surprising and unexpected result of the provision of axial magneticfocusing has been a conspicuous improvement in the resolution of thestored image written onto the storage screen by the writing beam, whichwhencombined with the improvement in the resolution in the image sectionprovided by the axial focusing field, provides substantially improvedresolution of the displayed image. This is believed to be attributableto the fact that 1n a solenoidal focusing field, magnification is unity,whereas in the case of the usual electrostatically focused writingelectron gun, the object-to-len-s distance is significantly less thanthe len-s-to-storage screen distance which `gives rise to amagnification of the spot produced on the storage screen by the writingbeam.

While I have described above the principles of my invention inconnection with specific apparatus, it is to be clearly understood thatthis description i-s made only by way of example and not as a limitationto the scope of my 1nvention.

What is claimed is:

1. In asignal-to-image display storage tube having a display screen andapertured charge storage screen means spaced from said display screen:means for forming and directing concentric pencil and flood electronbeams toward said storage screen means; magnetic deflection means actingupon both `of said beams for scanning the same over said storage screenmeans; means for modulating said pencil beam in accordance with an inputsignal whereby said pencil beam writes a charge pattern on said storagescreen means corresponding to said input signal and said flood beampasses through the apertures in said storage screen means to saiddisplay screen :being modulated by said charge pattern; and lmeans forproviding a magnetic viield extending axially between said displayscreen and said beam forming and directing means for focusing saidpencil beam onto said storage screen means and said modulated ood beamonto said display screen.

2. A signal-to-image display storage tube comprising: an evacuatedenvelope having a longitudinal axis and spaced lopposite ends; aphosphor display screen in said envelope at one end thereof and normalto said axis; rst electron gun means in said envelope at the other endthereof and concentric with said axis for for-ming and directing apencil electron beam toward said one end of said envelope; secondelectron gun means in said envelope at said other end thereof normal toand concentric with said axis for forming and directing a flood electronbeam toward said one end of said envelope-apertured charge storagescreen means in -said envelope between said ends and normal to saidaxis; deflection means acting' upon both of said beams for scanning thesame over said storage screen means; means for modulating said pencilbeam in accordance with an input signal whereby said pencil beam writesa charge pattern on said storage screen means corresponding to ysaidinput signal and said flood beam passes through the apertures in saidstorage screen means to said display screen being modulated by saidcharge pattern; and means for providing a magnetic field extendingaxially through said envelope and parallel with said axis for focusingsaid pencil beam onto said storage screen means and said modulatedIflood beam onto said display screen.

3. The tube of claim 2 wherein said second electron gun means includes aplanar cathode normal to said axis and having an aperture thereinconcentric with said axis through which said pencil beam passes.

4. The tube of claim 2 wherein said deflection means is magnetic and ispositioned between said second electron gun means and said storagescreen means.

5. The tube of claim 2 wherein said magnetic field is solenoidal.

6. The tube of claim 2 wherein said means for providing a magnetic fieldcomprises a solenoid coil surrounding said envelope and extendingsubstantially between said ends thereof.

7. A signal-to-image display storage tube comprising: an evacuatedenvelope having a longitudinal axis and spaced opposite ends; a phosphordisplay screen in said envelope at one end thereof and normal to saidaxis; rst electron gun means in said envelope at the other end thereofand concentric with said axis for forming and directing a pencilelectron beam toward said one end of said envelope; second electron gunmeans in sai-d envelope between said first elect-ron `gun means and saidone end and including a planar cathode normal to and concentric withsaid axis for forming and directing a flood electron beam toward saidone end of said envelope, said planar cathode having an apertureconcentric with said axis through which said pencil beam passes;apertured charge storage screen means between said planar cathode andsaid one end and normal to said axis; magnetic deflection means on theexterior of said envelope and between said planar cathode and `saidstorage screen means and actin-g upon both of said beams for scanningthe same over said storage screen means; means for modulating saidpencil beam in accordance wit-h an input signal whereby said pencil beamwrites a charge pattern on said storage screen means corresponding to`said input signal and said flood beam passes through the apertures insaid storage screen means to said display screen being modulated by saidcharge pattern; and a solenoid coil surrounding `said envelope and saidmagnetic deection means and extending substantially between said ends`for providing a solenoidal magnetic field extending axially through saidenvelope and parallel with said axis for focusing lsaid pencil beam ontosaid storage screen means and sai-d modulated flood beam onto saiddisplay screen.

8. The tube of claim 7 further comprising a screen electrode in saidenvelope adjacent said display screen and normal to said axis forincreasing the transit time of the flood beam electrons between saidstorage screen means and said display screen.

9. The tube of claim 8 further comprising a plurality of ring electrodesconcentric with ysaid axis and axially spaced apart between said storagescreen means and screen electr-ode for evenly dividing the potentialbetween said storage screen means and said screen electrode.

10. The tube of claim 7 wherein said first electron gun means includes acathode and control and accelerating electrodes positioned between saidother end and said second electron lgun means.

11. The tube of claim 7 wherein the axial distance from said storagescreen means to said display screen is substantially equal to anintegral number of full loops of focus of said flood beam, and whereinthe axial distance from said storage screen means to said first electrongun means is substantially equal to an integral number of full loops offocus of said pencil beam.

12. The tube of claim 7 wherein said second electron gun means includeselectrode means in said envelope between said planar cathode and saidstorage screen -means for providing planar accelerating equipotentialsfor said flood beam.

References Cited by the Examiner UNITED STATES PATENTS 3,087,088 4/1963Hunter 315-12 DAVID G. REDINBAUGH, Primary Examiner. T. A. GALLAGHER,Assistant Examiner.

1. IN A SIGNAL-TO-IMAGE DISPLAY STORAGE TUBE HAVING A DISPLAY SCREEN ANDAPERTURED CHARGE STORAGE SCREEN MEANS SPACED FROM SAID DISPLAY SCREEN:MEANS FOR FORMING AND DIRECTING CONCENTRIC PENCIL AND FLOOD ELECTRONBEAMS TOWARD SAID STORAGE SCREEN MEANS; MAGNETIC DEFLECTION MEANS ACTINGUPON BOTH OF SAID BEAMS FOR SCANNING THE SAME OVER SAID STORAGE SCREENMEANS; MEANS FOR MODULATING SAID PENCIL BEAM IN ACCORDANCE WITH AN INPUTSIGNAL WHEREBY SAID PENCIL BEAM WRITES A CHARGE PATTERN ON SAID STORAGESCREEN MEANS CORRESPONDING TO SAID INPUT SIGNAL AND SAID FLOOD BEAMPASSES THROUGH THE APERTURES IN SAID STORAGE SCREEN MEANS TO SAIDDISPLAY SCREEN BEING MODULATED BY SAID CHARGE PATTERN; AND MEANS FORPROVIDING A MAGNETIC FIELD EXTENDING AXIALLY BETWEEN SAID DISPLAY SCREENAND SAID BEAM FORMING AND DIRECTING MEANS FOR FOCUSING SAID PENCIL BEAMONTO SAID STORAGE SCREEN MEANS AND SAID MODULATED FLOOD BEAM ONTO SAIDDISPLAY SCREEN.